An automatic lathe comprises, in addition to a headstock which rotates the workpiece and a tailstock which can support the workpiece for such rotation, a tool-carrying mechanism which can be in the form of a turret provided with a plurality of spaced-apart tool-carrying stations at each of which a respective tool can be positioned vis-a-vis the workpiece by rotation of the turret about a turret axis, manually or automatically in accordance with a predetermined program for successive oerations of the tools on the workpiece and in a cycle through which the turret can be rotated.
Many of the tools carried by the turret are fixed on the turret body, but for certain kinds of operations on the workpiece it is convenient to have rotatable tools mounted on the same turret, i.e. tools which can be rotated around their axis, in order to make operations like milling, drilling, boring, threading and the like. Without such kind of rotatable tools, for these operations it is necessary to remove the workpiece from the lathe and mount it on another machine.
In order to avoid this extra handling of the workpiece it has been proposed to provide turrets carrying some tools which can be driven in rotation to make the cited operations.
For this purpose turrets are known which are equipped with external drive mechanisms to rotate the tools, but these systems occupy considerable space and are generally of complex structure. Because of the space occupied by such external drives, difficulties may be encountered in locating the tool with respect to the workpiece.
In another kind of turret a common drive is provided for all of the rotatable tools; these turrets drive contemporarily all the rotatable tools, and not only the one in working position on the workpiece.
These turrets have the drawback that additional protective device must be provided in order to prevent accidental contact of the operator with the rotating tools which are not in contact with the piece, thereby forming an additional encumbrance.